They consist of lipophilic and hydrophilic portion separated by a connecting hydrocarbon chain. The hydrophilic portion is a tertiary amine, such as diethylamine, whereas the lipophilic portion is usually an unsaturated aromatic ring, such as paraaminobenzoic acid. In almost all instance, an ester (-CO-) or and amide (-NHC-) bond links the hyrdocarbon chain to the lipophilic aromatic ring.

Which of the local anesthetics are chiral?

Mepivicaine, Bupivacaine, Ropivacaine, and Levobupivacaine (these are all amides too!)

It consists of a large sodium conducting pore (aplha subunit) with varying numbers of adjacent smaller beta subunits. The alpha is divided further into 4 subunits. H is the alpha subunit that allows ion conduction and binds to local anesthetics.

Lidocaine, Prilocaine, and Bupivacaine--> limits the concentration of drug that reaches systemic circulation

How is lidocaine metabolized?

Through oxidative dealkylation in the liver to monoethylglycinexylidide (has 80% of activity of lidocaine for protecting against cardiac dysrhythmias) followed by hydrolysis of this metabolite to xylidide

What is prilocaine metabolized to and what is the concern with this metabolite?

Orthotoluidine. It is an oxidizing compound that is capable of converting hemoglobin to its oxidized form, methemoglobin. Prilocaine >600mg can cause sufficient methemoglobin to make the patient appear cyanotic and decrease oxygen-carrying capacity.

Alpha1-acid glycoprotein (concentration of this protein is increased in many situations including post-op traumas; ropivacaine binds to this protein too)

Which of the amide locals do not cause much vasodilation and thus dont need epinephrine in mixture?

Prilocaine
Mepivacaine

Which local anesthetic is the most slowly eliminated?

Dibucaine

How is ropivacaine metabolized?

It is metabolized to 2,6-pipecoloxylidide and 3-hydroxyropivacaine by hepatic CYTOCHROME P-450 enzymes; less than 1% is excreted unchanged in urine (dosage adjustments to renal impairment may not be necessary but in pts with uremia the 2.6 metabolite may accumulate and be toxic)

How are ester local anesthetics metabolized?

They undergo hydrolysis by cholinsterase enzyme principally in the plasma and to a lesser extent in the liver. The rate of hydrolysis varies with chrlorprocaine being the most rapid, procaine being intermediate, and tetracaine being the slowest. The metabolites are inactive although paraaminobenzoic acid may be an antigen responsible for allergic reactions.

What is the exception to the ester local anesthetic metabolism in plasma?

Cocaine which undergoes metabolism mainly in the liver.

What is benzocaine good for and why?

It is ideal for topical anesthesia because it is a weak acid and exists nonionized at physiologic pH--rapid onset and duration of action of 30-60 minutes
*Methemoglobinemia is rare but a potential complication

What is the benefit of mixing epinephrine in local anesthetic solutions?

It produces vasoconstriction which limits systemic absorption (by 1/3) and lengthens the duration of action (not used with ropivacaine)

What are the principal side effects related to the use of local anesthetics?

Numbness of tongue and circumoral tissue, restlessness, vertigo, tinnitus, difficulty in focusing; more dosage results in slurred speech and skeletal muscle twitching that first evident in face and extremities--> tonic clonic seizures

What is the treatment for local anesthetic induced seizures?

Ventilation of lungs with oxygen because arterial hypoxemia and metabolic acidosis can occur in seconds. Also IV administration of a benzodiazepine such as midazolam and diazepam is effective in suppressing local anesthetic-induced seizures.

What are transient neurologic symptoms?

Moderate to severe pain in lower back , buttocks, and posterior thigh that appears 6-36 hours after complete recovery from single-shot spinal anesthsia and full recovery may take between 1 and 7 days.

It is a 5% combination of lidocaine-prilocaine cream that is used for skin grafting, venipuncture, arterial cannulation, lumbar puncture, myringotomy in children, circumcision

What is the benefit of dyclonine?

It is used to provide topical anesthesia of the airway in a patient that is presumed to be allergic to bupivacaine and procaine.

How is peripheral nerve block anesthesia achieved?

By injection of local anesthetic solutions into tissues surrounding individual peripheral nerves or nerve plexuses such as brachial plexus.

Which locals are recommended for IV regional anesthesia?

Lidocaine, prilocaine, mepivacaine

How is epidural anesthesia done and how does it work?

Local anesthetic solutions are placed in the epidural or sacral caudal space. They first diffuse across dura to act on nerve roots and spinal cord then it also diffuses into the paravertebral formania producing multiple paravertebral nerve blocks.

How is spinal anesthesia produced?

It is produced by injection of local anesthetics into the lumbar subarachnoid space; principal site of action are the preganglionic fibers as they leave the spinal cord in the anterior rami

What is tumuscent liposuction?

Subcutaneous infiltration of large volumes (5 or more liters) of solution containing highly diluted lidocaine with epi (1:100,000)--> sufficient local anesthesia for liposuction and prolonged post-op analgesia